The present invention relates to control of movement of a head in a storage device which can use a medium having concentric or spiral tracks. More particularly, the invention relates to head position control in storage devices having a plurality of guard areas which do not include position information (ID).
In recent years, disk type computer media such as phase change type disks and magneto-optical disks or the like are being developed, in addition to floppy disk, hard disk and card/tape type optical storage technology.
In comparison with a floppy disk or a hard disk, an optical disk is capable of drastically increasing the recording capacity by forming recording pits of the sub-micron order on the medium, using a laser beam.
Moreover, information rewriting of a hundred thousand times or more is possible for a magneto-optical disk utilizing a rare earth-transition metal based material, and expectations are high for this magneto-optical disk. Recently, development has been made for such an optical disk having storage capacity of 540 MB to 640 MB at one surface of a 3.5 inch disk.
The storage capacity of a typical floppy disk of 3.5 inch is about 1 MB, so the storage capacity of an optical disk is equal to that of 540 to 640 floppy disks. As described, an optical disk is a rewritable storage medium having a much higher recording density.
However, the recording density of an optical disk must be further raised from the current density, in preparation for the future multi-media era. In order to raise the recording density, more pits must be recorded on the medium. Therefore, the current pit must be further reduced in size and the interval between pits must also be reduced.
In the case of raising the recording density with such a method, the wavelength of the laser beam has to be further reduced from the current 670 nm, but when practical use is considered, the pit size must be reduced even in the current wavelength of 670 nm.
It is possible to form the pit smaller than the beam diameter by controlling the power of the laser beam when recording. However, in regard to reproduction, when a pit smaller than the beam diameter is formed, crosstalk with a neighboring pit increases. In the worst case, the neighboring pit is entered in the reproduced beam. Thus, normal reproduction is very difficult when practical use is considered.
As a method for reproducing the pit smaller than the beam diameter in the current wavelength of 670 nm, MSR (Magnetically induced Super Resolution) has been proposed. The principle of MSR, namely rare earthxe2x80x94transmission metal based film material of a magneto-optical recording medium layer consisting of a reproducing layer, a switch layer (intermediate layer) and a recording layer, and a method of manufacturing a magneto-optical storage medium, are disclosed in detail in Japanese Published Unexamined Patent Application Nos. HEI 7-244877, HEI 9-147436 and HEI 10-134429, and others.
An optical storage medium used in an optical disk apparatus has, as illustrated in FIG. 1, concentric or spiral tracks divided into a plurality of sectors. The sectors are alternately provided with recording areas (DATA areas) for recording and/or reproducing data and header areas (ID area) formed of the recessed and projected pits.
In the ID area, a sector mark (SM) indicating the position of a sector, position information (ID information) such as track number, sector number, etc. and VFO such as a synchronous pattern are recorded.
The target sector of the target track can be positioned by the relative movement (tracking) of the head in the traveling direction (track following direction) 121 with rotation of the optical storage medium.
Moreover, the operation for moving the head with a carriage or lens actuator (track actuator) in the direction (disk medium radius direction) 123 crossing the tracks in order to move the head to the target track at a high speed to record/reproduce the information on the medium is called the seek operation.
Under the seek control, when the ID (track No., sector No.) is issued, as the target position of movement, via an interface controller from a host, the optical disk apparatus immediately reads the ID (track No., sector No.) of the current position with the carriage 122 in order to identify the current position.
The amount of movement required, i.e., the difference between the target position and the current position, is calculated with the MPU. This amount of movement is converted to the number of tracks to be jumped and it is then set to a DSP (Digital Signal Processor) as a VCM (Voice Coil Motor) drive controlling means for driving the carriage 122. Therefore, the carriage executes the seek operation in the traveling direction 123 by instructing a drive current of the VCM from the DSP via the driver.
For the storage medium of the related art, ID exists for all tracks in the range where the head moves, namely in the track jump range of the track actuator in which the lens can precisely move in the track crossing direction and in the seek range of the carriage. Therefore, the current position (track No., sector No.) can be detected immediately by reading the ID.
In these years, a high density storage medium in which track interval is reduced from the current interval to form more tracks by utilizing the MSR technology is being developed. Almost all optical disk media employ the ZCAV system, in which a predetermined number of tracks are defined as one zone and control for making the angular velocity constant is performed for a plurality of zones.
The latest high density storage medium technology has a problem in the recording, erasing and reproducing operations at the boundary of zones, due to realization of higher track density.
Therefore, as illustrated in FIG. 2, guard areas are provided between zones of tracks (track grooves are formed like ordinary tracks) but the ID area and DATA area do not exist in the track at the boundary of zones. Accordingly, the number of guard areas depends on the number of zones.
Guard areas prevent interference with respective tracks of neighboring zones, and are used because track density is higher than it is in the related art. Namely, about 10 tracks are provided in one guard area. Although it is a matter of course, the data areas in the ordinary tracks have the ID area and DATA area as in the case of FIG. 1.
When the head is positioned (on-track) to this guard area in the seek method of the related art, since ID does not exist, as illustrated in FIG. 3, an error that ID cannot be read is judged and therefore the ordinary error recovery process, which is based on the to existence of ID, is executed.
However, in the high density storage medium of the new system, ID cannot be read even with any kind of method because the ID does not intrinsically exist. Accordingly, the track number and sector number cannot be recognized and error recovery is conducted for a long period of time. As a result, time is wasted. In addition, a seek error is also generated, lowering reliability of the medium and apparatus.
FIG. 3 illustrates the recovery process when ID cannot be read in the medium of the related art. The ordinary recovery process means this flowchart. The step S1 indicates that the target track is instructed and seek is completed. In order to detect the seek end position, the ID is read in step S2.
As a result, operation transfers to the ordinary process when ID can be read in step S3. If ID cannot be read, the recovery process starts from step S4. Factors for searching for the cause of error are sequentially detected.
In step S4, it is determined whether or not forcible ejection is occurring. If it is a cause, exclusive recovery is conducted. When it is not a cause, whether LD is erased or not is detected in step S5.
When it is not a cause, it is detected in step S6 whether or not the spindle is stopped. If it is a cause, exclusive recovery is conducted. When it is not a cause, whether VCM over-current is detected in step S7. If that is a cause, exclusive recovery is conducted. When it is not a cause, defocusing is detected in step S8.
If defocusing is a cause, exclusive recovery is conducted. When it is not a cause, out of track condition is detected in step S9. If an out of track condition is a cause, exclusive recovery is conducted. When a factor is not yet detected even in this step, the recovery process is not conducted, and initialization is conducted to prepare for another recovery process if needed. Track control is turned off in step S10. Focus control is then turned off in step S11.
VCM initialization is conducted in step S12. Focus control is turned on in step S13. Track control is then turned on in step S14. Thereafter, ID is read again in step S15. When ID is read in step S16, the process is completed normally. If ID cannot be read normally, retry is conducted after returning to (1).
Since the guard area of the latest high density medium is in the track where the ID does not exist, when the recovery process of the related art is conducted, even if retry is repeated many times after returning to (1), ID cannot be read. Therefore, head position, namely optical beam position, cannot be recognized and more time is wasted, which of course has an adverse effect on the seek process.
The amount of seek can be measured by detecting the number of tracks which are crossed by the head, but as track density increases, and moreover as the moving distance (difference) of the head increases in the seek operation, the possibility for detection mistakes increases.
Namely, when the difference is large and the target track is set to the area near the guard area, the head is liable to seek the guard area and enter the guard area erroneously.
It is therefore an object of the present invention to provide a storage device which can realize high speed access to the target position with higher reliability even with higher density tracks and guard areas in the medium by not seeking to guard, avoiding erroneous seeks to guard areas when seeking an area near the guard area, and by conducting recovery control when seek is conducted to the guard area.
A storage device of the present invention can use a storage medium including a data area having position information at least indicating the position to reproduce data, and a guard area not having the position information. The storage device includes a head for reproducing at least data, a head driving means for moving the head from a current (or initial) position to a target position on the storage medium, and a control means for controlling the drive of the head driving means by instructing the head to move up to the target position from the current position. Throughout this specification, the terms xe2x80x9ccurrent positionxe2x80x9d and xe2x80x9cinitial positionxe2x80x9d are both used interchangeably to refer to the starting position of the head, with respect to the medium, prior to moving the head in a track jump or seek operation. In the preferred embodiment of the present invention, the control means controls the drive of the head driving means by instructing the driving means to prevent the head from being moved to the guard area when the storage medium is a storage medium having a guard area.
Moreover, when the target position is set at an area near the guard area, the control means instructs the amount of compensated movement obtained by directing the amount of compensation needed for movement up to the target position from the current position of the head.
Moreover, the control means instructs, as the moving control condition, the amount of compensated movement obtained from the amount of compensation, determined depending on the amount of movement up to the target position from the current position of the head.
In addition, the control means assures that the amount of compensated movement when the amount of movement is large is larger than the amount of compensated movement when the amount of movement is small.
In one embodiment, the control means does not conduct movement of the head by the head driving means and issues an error when the instruction to move the head to the guard area is issued from a host.
In another embodiment, the control means controls the drive of the head driving means, when the head is positioned in the guard area, by instructing movement of the head to the data area from the guard area.
In still another embodiment, the control means causes the guard area to draw back by controlling the head to follow the spiral track for a predetermined period of time.